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Subject: Re: problem with netCDF4 OpenDAP
From: Jason Swails <jason.swails@gmail.com>
In-Reply-To: <d35j2uFp5hdU1@mid.individual.net>
Date: Fri, 14 Aug 2015 09:15:17 -0400
Cc: python-list@python.org
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To: Tom P <werotizy@freent.dd>
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> On Aug 14, 2015, at 3:18 AM, Tom P <werotizy@freent.dd> wrote:
>=20
> Thanks for the reply but that is not what the documentation says.
>=20
> http://unidata.github.io/netcdf4-python/#section8
> "Remote OPeNDAP-hosted datasets can be accessed for reading over http =
if a URL is provided to the netCDF4.Dataset constructor instead of a =
filename. However, this requires that the netCDF library be built with =
OPenDAP support, via the --enable-dap configure option (added in version =
4.0.1).=E2=80=9D

=E2=80=8BHuh, so it does.  Your error message says "file not found", =
though, which suggested to me that it's trying to interpret the NetCDF =
file as a local file instead of a URL.  Indeed, when I run that example, =
the traceback is more complete (the traceback you printed had omitted =
some information):

>>> =
netCDF4.Dataset('http://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v3b/netcdf/e=
rsst.201507.nc')
syntax error, unexpected WORD_WORD, expecting SCAN_ATTR or SCAN_DATASET =
or SCAN_ERROR
context: <!DOCTYPE^ HTML PUBLIC "-//IETF//DTD HTML =
2.0//EN"><html><head><title>404 Not Found</title></head><body><h1>Not =
Found</h1><p>The requested URL =
/pub/data/cmb/ersst/v3b/netcdf/ersst.201507.nc.dds was not found on this =
server.</p></body></html>
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "netCDF4/_netCDF4.pyx", line 1547, in =
netCDF4._netCDF4.Dataset.__init__ (netCDF4/_netCDF4.c:9551)
RuntimeError: NetCDF: file not found

So it=E2=80=99s clear that netCDF4 is at least *trying* to go online to =
look for the file, but it simply can=E2=80=99t find it.  Since the docs =
say it=E2=80=99s linking to libcurl, I tried using curl to download the =
file (curl -# =
http://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v3b/netcdf/ersst.201507.nc =
> test.nc) and it worked fine.  What=E2=80=99s more, it *seems* like the =
file (/pub/.../ersst.201507.nc.dds) was decorated with the =E2=80=98.dds=E2=
=80=99 suffix for some reason (not sure if the server redirected the =
request there or not).  But this looks like a netCDF4 issue.  Perhaps =
you can go to their project page on Github and file an issue there -- =
they will be more likely to have your answer than people here.

HTH,
Jason

>=20
> and for the Anaconda package -
> http://docs.continuum.io/anaconda/changelog
> "2013-05-08: 1.5.0:
> Highlights:
>  updates to all important packages: python, numpy, scipy, ipython, =
matplotlib, pandas, cython
>  added netCDF4 (with OpenDAP support) on Linux and MacOSX"
>=20
> --=20
> https://mail.python.org/mailman/listinfo/python-list

--
Jason M. Swails
BioMaPS,
Rutgers University
Postdoctoral Researcher